This is a 371 of International Patent Application No. PCT/DE96/01275, filed Jul. 8, 1996.
The present invention concerns novel water-soluble polyammonium salts, branched in a specific way, with high molecular weight and a process for their preparation. Such polymers are useful in water purification processes.
The increasing application of water-soluble, cationic polymers and copolymers in methods for waste water treatment, such as the dewatering of sludge or purification of contaminated water is leading to new developments in the area of synthesis of new types of polyammonium salts.
The effectiveness of using highly cationic polymers depends on the molecular weight of the polymer, on the nature of the selected monomer and on the architecture of the polymer chain.
The synthesis of water-soluble, polymeric, quaternary ammonium salts by free-radical polymerization is known and leads to linear polymer structures. An example of this is the solution polymerization of diallyldimethylammonium chloride (DADMAC), which is described in U.S. Pat. No. 3,288,770 or in DD Patent 127,729.
In order to obtain special product properties or to synthesize polymers with higher molecular weight, copolymerization with polyfunctional crosslinking comonomers are used. Mixtures of the ammonium monomer with bisallyl esters of dicarboxylic acids are polymerized in aqueous solution with free-radical initiation (DD Patents 127,729, 128,189 or 128,247). Such branched structures are also obtained in agreement with the teaching of FR Patent 1,494,438 or U.S. Pat. No. 3,544,318. Here, triallyl- or tetraallylammonium salts are used as chain-branching agents. The necessary small amounts of chain-branching agents are added to the batch at the beginning of the polymerization. It is well known that at concentrations of the polyfunctional monomer of more than 0.1%, the obtained polymer is partially or completely crosslinked. This leads to a polymer which is insoluble in the solvent (Vollmert, Grundriss der Makromolekularen Chemie, Springer-Verlag, Berlin, 1962,p. 196). In EP Patent 0,264,710, an improved method is presented for the copolymerization of DADMAC with such polyfunctional monomers. If a dosage method is used for the comonomer, the comonomer can be incorporated to a greater extent. In this way, polymers with higher molecular weight are obtained and the risk of gelling during the polymerization is reduced. In general, a fairly complicated addition program must be followed in order to obtain a successful polymerization result.
In all cases in which polyfunctional, crosslinking comonomers are used as agents for increasing the molecular weight, there is still a processing risk because of the possibility of gel formation. On the other hand, one cannot avoid producing, in addition to highly branched polymer chains with high molecular weight, macromolecules with a lower degree of polymerization. Because of the reduced activity in practical applications of the poly-ammonium salt, the fraction with low-molecular weight is disadvantageous.
Branched polymers can also be synthesized by a graft copolymerization method. This method was also used for the synthesis of DADMAC-acrylamide copolymers (G. B. Butler, J. Macromol. Sci. A26, 681 (1989)). A copolymer of DADMAC and dihydroxyalkyl derivatives of acrylic acid is synthesized as a prepolymer and then, using Ce4+ salts as initiator, free-radical grafting of acrylamide or a mixture of acrylamide and DADMAC onto the prepolymer is achieved. In all cases, high concentrations of the prepolymer are needed in order to obtain polymer yields of about 80%. This is unacceptable from an industrial point of view.
Branched copolymers of acrylamide and cationic monomers, such as cationic, modified acrylate esters or acrylamides or diallylammonium salts are synthesized in a similar way by copolymerization of acrylamide with macromonomers of the cationic functionalized monomer having a double bond as the terminal group, as described in U.S. Pat. No. 5,211,854.
It is the task of the present invention to develop novel, water-soluble polymers, quaternary ammonium salts with DADMAC in particular as repeating unit of the polymer chain, which are characterized by a comb-like structure, in which the DADMAC-amine copolymer or any other water-soluble polyamine containing charged units represents the rigid backbone chain and the quaternary ammonium salt, preferably DADMAC, is arranged as chain units in side chains suspended on the backbone. Another task is to propose a method for their preparation.
The task is solved with regard to the polyammonium salt by the characterizing features of claim 1 and with reference to the method by the characterizing features of claim 8. The Subclaims show advantageous further developments.
The branched polyammonium salt with high-molecular weight according to the invention consists of unsaturated quaternary ammonium compounds and suitable prepolymers containing linear amine groups, in which the prepolymer represents the backbone and the ammonium salt forms the side chain. In the polyammonium salt according to the invention, 0.1 to 30 mole % of the prepolymer sequencexe2x88x92[Axe2x80x94Bxe2x80x94NR]nxe2x80x94represents the backbone and 70 to 99.9 mole % of the quaternary ammonium salt represents the side chain. The prepolymer sequence that forms the backbone chain is selected from polyampholytes, copolymers of diallyldimethylammonium chloride and a polymerizable amine compound, polyamideamine and DADMAC. The quaternary ammonium salt is attached as chain element to the amine-group-containing prepolymer. The comb-like branched polyammonium salt can be represented by the following general formula I: 
where C represents the quaternary ammonium salt side chain.
The comb-like polyammonium salt has a degree of polymerization which is chosen in such a way that a molecular weight  greater than 100,000, preferably  greater than 250,000 g/mole results. The degree of polymerization n of the prepolymer is chosen so that a molecular weight of the linear, amine-group-containing prepolymer is in the range between 10,000 and 100,000 g/mole.
It is preferable when the amine-group-containing prepolymer sequence is chosen from compounds having the following formulas 2 to 4: 
with Z=xe2x80x94OH, xe2x80x94NRR1 and
R=H or alkyl-
R1=H, alkylxe2x80x94or aryl- 
In the preferred prepolymers of general formula 2, the degree of polymerization n, m and n, p is chosen in such a way that a molecular weight of 10,000 to 100,000 g/mole results, where the ratio n:m and n:p is in the range from 1:1 to 95:1.
Furthermore, it is preferable when the prepolymer is a DADMAC polymer with 0.5 to 5 mole % of triethanolamine units.
The novel, water-soluble, comb-like, polymeric, quaternary ammonium salts are polymers based on unsaturated quaternary ammonium salts and especially DADMAC, as well as on a suitable water-soluble prepolymer that consists of at least 1 mole % to 100 mole % of amine function-containing compounds as repeating unit in the rigid prepolymer chain.
Futhermore, the invention is concerned with a method for the preparation of a water-soluble high molecular weight quaternary ammonimn graft polymer wherein quaternary ammonium salt side chains are grafted onto a polyamine backbone polymer under ree radical conditions, wherein the initiator system comprises a free radical-producing oxidizing agent and the polyarine backbone polymer. Preferably, the polymerization is carried out with 30-65 weight percent solutions in water of the monomer at temperatures of 15-65xc2x0 C., wherein the polyamine backbone consists of 1-100 mole percent amine function containing units and wherein the polyamine backbone polymer has a molecular weight of 10,000 to 100,000 g/mole.
When using the present invention, novel, comb-like polyammonium salts with average molecular weights of greater than 100,000,preferably 250,000 and even more preferably  greater than 500,000 g/mole are obtained; in addition, the prepolymer is completely embeded in the final polymer and the amount of homopolymer is insignificantly small.
Due to the new comb-like architecture, which consists of the rigid polyamine-group-containing backbone and cationic attached macromolecular side chains, the obtained novel copolymers differ from the polyammonium salts of the state of the art by a number of characterizing properties. The fundamental structure of the prepolymer can be detected in the final product. It is possible to control the molecular weights of the copolymers by the molecular weights and the concentration of the grafting points of the prepolymer. Furthermore, the number of attached chains can be controlled by the concentration of the graftable functional groups in the prepolymer. In this way, there is a great variation in order to adapt the properties of the comb-like polyelectrolytes in solution (the solution property is the significant interaction parameter for industrial applications of these polymers).
The drastic increase of the intrinsic viscosities during polymerization is also a characteristic property of the novel polymers. For DADMAC as cationic monomer of the polymer synthesis of the present invention, the copolymers are characterized by being insoluble in methanol.